Ducane furnace will not light then shuts down

I have a Ducane Furnace model # MPGA07583A. When I turn on the thermostat the exhaust fan turns on for about 25 seconds then the unit shuts down. The error code blinks 3 times then hesitates then blinks again 3 times. The igniter does not glow and the main fan does not turn on. Right before this problem the igniter would glow, the burners would ignite and the main fan would run for about 25 seconds and then the unit would shut down. The green light on the control then blinks an error code 3 times. I replaced the flame sensor and that did not work.

Any help or ideas on what I might try next or what parts might need replacing would be greatly appreciated. Thanks in advance.

You need a new ignitor. The fan isn't supposed to turn on until the plenum gets warm. It's supposed to shut down the whole thing if the flame sensor doesn't detect anything after ten seconds or so. The ignitor would come on even if the gas valve was bad - so I'd say it's the ignitor.